As a designer for the Industry, I have so stand my ground on this. Yes we design custom uniforms, but it is the clients vision, not ours. 90% of the design process starts with the gym owners vision. Yes we will do our best to make them look great and match the theme of every gym, but it's not always easy. So when it comes to mesh stomaches, it is not the designer to blame. The gym owner wanted and requested it. A lot of it has to do with their budget too. They will want a gorgeous crop top, but then with the full top they don't have much of a budget left to get creative and have different panels of different fabrics.